This disclosure relates to the field of water purification, and in particular provides a biocidal water purification method and apparatus configured to apply ionizing radiation to a flow of water at close range.
Rendering water fit for human consumption for purposes of ingestion, but also for washing and cooking, may involve treatment to eliminate biological contaminants and pathogens. The water treatment steps that need to be undertaken vary with the content of the source water to be treated. For example, fresh water from a spring or stream needs less extensive treatment than water that has been compromised by flood or sewage. But even seemingly clean fresh water, especially from streams or rivers or from sources that may have been flooded, may be compromised by suspended particles, parasites, bacteria, algae, viruses, fungi and the like, often as a result of a failure of human sanitation. These pathogens and parasites are responsible for various water borne diarrheal and other illnesses.
A complete municipal water purification plant is capable of eliminating chemical and biological threats. Chemical reaction with particular reagents such as flocculation agents, followed by skimming and sedimentation, filtration to remove undissolved solids, ultra filtration and/or reverse osmosis filtration to remove dissolved solids (salts), and chlorination to preserve the treated water are all known. But a complete and operational water purification plant may not be available or feasible, in which case a smaller, and even portable, water purification apparatus is useful.
The physical and chemical facilities needed for municipal water treatment may be substantial and complex, having large fixed installations with ponds, tanks, pumps, filtration beds, skimmers, backwashes, controls, etc. A challenge is presented to accomplish similar treatment steps in a compact unit. In the case of porous media or reverse osmosis filtration, electric power is needed to develop a sufficient pressure head. Chemical water treatment process steps that might be considered as candidates, such as ozonation (sparging with ozone gas), chlorination at concentration sufficient to oxidize organic molecules, and similar water treatment processes may employ strong chemicals that would be unmanageable in a small water treatment unit intended to be portable and safe. Chemicals with high oxidation potential are likely to be unhealthful for human exposure.
With respect to ozonation, for example, the technique is to expose treatment water temporarily to ozone gas and to collect the excess ozone reagent. But ozone is corrosive and is considered poisonous. Leaks carry a risk of fire. Ozone and other elements and compounds that act as biocides, or that degrade organic molecules, may be poisonous to humans or have high oxidation potentials making them dangerous or difficult to store and handle. Even if safely handled, such chemicals may produce undesirable reaction products when certain compositions are present in the treatment water.
A small water purification system is desirable for applications that require a small processing capacity. An advantageous system would be lightweight, compact and portable. If used for processing relatively fresh water from a natural source such as a stream or body of water, the processing can be limited to pore filtration and a biocidal treatment. The biocidal treatment eliminates the viability of pathogens (microbes, viruses, bacteria, bacterial or fungal spores, parasites and the like).
Devices that emit UV light in a particular frequency range are also used for biocidal treatment of water. The frequency is chosen to optimize the destruction of chemical bonds in proteins and DNA molecules within the target organisms in the water. UV treatment also requires considerable electrical power and equipment to achieve the required kill levels.
Electron-beam radiation is a form of ionizing energy. The beam, is a concentrated, stream of electrons, accelerated by a high voltage source to energy levels in the MeV range. The electrons strike a target and produce high flux levels of x-rays primarily from the bremsstrahlung process. E-beam systems are now perceived as a cost-effective means for biocidal treatment of waste and municipal water. Like UV sources the objective is to have the x-rays break chemical bonds in the target organisms. The apparatus is energy intensive, subject to routine repair, and is complex.
It would be advantageous to provide a water treatment apparatus and technique that is at or near 100% biocidal in one exposure step, that also degrades or eliminates even nonviable organic compounds that might lead to immunologic or allergenic reactions, that is small, safe, does not use electric power, can be operated easily without extensive training, and does not involve adding strong or possibly noxious chemicals to the water.
Solutions are needed for water treatment, in particular to provide a biocidal water treatment step in an apparatus that can be compact, lightweight, low or zero in requirements for electrical power, and devoid of chemicals that are poisonous or have high oxidation potentials.